Background: The function of the Ras association domain family 1 (RASSF1)/modulator of apoptosis 1 (MOAP-1) molecular tumor suppressor pathway is often perturbed in many solid and blood cancers by epigenetic loss of RASSF1A via promoter specific methylation. However, a detailed analysis of expression and stability of MOAP-1 as well as effect on cellular proliferation and cell death in blood cancers has not been explored.
Methods: Expression of MOAP-1 RASSF1A was performed by immunoblotting analysis, MOAP-1 effect on biology determined by cell proliferation, cell death and tumorigenicity assays. Lastly, proteomic analysis in MOAP-1 in form 1 and 2 expressing cells reveal new interacting partners to MOAP-1.
Results: The expression of MOAP-1 appears to be quite varied and exists as two forms, a p39 and p46 form in blood cancers. The higher MOAP-1 p46 form was mainly observed in acute myeloid leukemia (AML) and some acute lymphocytic leukemia (ALL) patients and cell lines. Furthermore, MOAP-1 p46 form can be reduced to the p39 form upon calf intestinal or lambda phosphatase treatment, suggesting post-translational phosphorylation likely produces the slower migrating form. Blood cancer cell lines containing the p46 form of MOAP-1 appears to be more resistant to cell death signals and have increased growth. In addition, we document in vivo protection from tumorigenesis of cells containing MOAP-1 following tail vein injection of cancer cells. Lastly, proteomic analysis revealed several interesting components of the MOAP-1 interactome in blood cancer cells that we validated.
Conclusions: MOAP-1 is a bona fide tumor suppressor in blood cancers with functions beyond apoptosis.